The present invention relates to a single car test device with which railway car brake systems are checked to assure proper operation without requiring removal of any of the brake system components from the car. More particularly, the invention is directed to a modified regulating valve of the single car test device for achieving more comprehensive test results.
Existing single car test devices are relatively simple in design and low in cost, employing a regulator valve that can be adjusted to supply a predetermined test operating pressure for charging the brake equipment when the outlet coupling of the single car test device is connected to a railway car brake pipe. The regulator valve typically used in this application is known commercially as the N-1 Reducing Valve. The brake pipe is charged from a source of compressed air through an operator's multi-position rotary valve that is situated between the regulating valve and the outlet coupling to the brake pipe. The different rotary valve positions provide different preselected rates at which the test operating pressure is supplied to the brake pipe from a source of compressed air and exhausted to atmosphere, in accordance with the prescribed test code. In a lap position of the rotary valve, this charging and venting of the brake pipe are both cut off.
Also employed in the existing single car test devices is a FLOWRATOR meter that is situated between the rotary valve and outlet coupling to provide a visual indication of the rate of air flow in the brake pipe when a bypass cock associated with the FLOWRATOR meter is closed. While the FLOWRATOR meter reading can be used to ascertain system leakage, only the leakage attributed to the brake pipe can be identified specifically by making a leakage test with the car control valve cut out. This is due to the fact that while the regulating valve of the single car test device has a pressure maintaining capability at its one full pressure setting, this pressure maintaining capability is nullified when the brake pipe pressure is reduced or the operator's valve is moved to lap position during a test, since the rotary valve cuts off the regulating valve from the car brake pipe in this lap position.
The Association of American Railroads has recently specified a change to the conventional single car test procedure, which in one important instance requires that a 10 psi maintained reduction of the test operating pressure reduction be made below the selected maximum test operating pressure setting. The specific purpose of this test is to better detect undesirable leakage into the car brake cylinder, which is critical to assuring proper brake control valve operation. It has been proposed by others to add to the capability of the single car test device to provide such a second pre-set pressure maintained 10 psi below the first pre-set test operating pressure by adding a by-pass line including a second regulating valve and a cut-out cock. By pre-setting this second regulating valve 10 psi below the main regulating valve pressure setting and opening the by-pass cut-out cock, with the by-passed operator's valve placed in lap position No. 3, the 10 psi maintained pressure reduction can be achieved.
This method for modifying the single car test device to provide this dual pressure maintaining requirement entails considerable additional valves, cocks, fittings, and piping, thus making the single car test device more complex to operate and maintain, more cumbersome to handle and considerably more expensive in both initial cost and maintenance, as well as likely adding to the incidence of breakdown.